1. Field of the Invention
The present invention relates to a multi-beam scanning apparatus that scans multiple-beams emitted from a plurality of light sources, such as semiconductor lasers. More precisely, the present invention relates to a separate control device for the plurality of light sources.
2. Description of the Related Art
In recent electronic photograph systems or printers, multi-beam scanning devices with a plurality of semiconductor lasers have been incorporated to form color-images. The number of lasers corresponds to the number of colors used for forming the color-image. For example, when Black, Cyan, Magenta, and yellow are used to form the image, four semiconductor lasers are required. To improve the process-speed of the system, generally, the plurality of semiconductor lasers is controlled simultaneously. Namely, the multiple-beams are simultaneously scanned. The scanning apparatus is composed of a scanning unit that has a plurality of semiconductor lasers and an optical system, and a controller that transmits image data to the scanning unit and controls the scanning unit. Generally, the scanning unit and the controller are separately constructed.
To obtain high-quality images with proper density, bias control and APC (Auto Power Control) are performed. The bias control is performed for improving modulation characteristics of a high-speed drive of a semiconductor laser, and the APC is performed for automatically controlling light-intensity of a semiconductor laser. The above controls must be performed separately for each of the plurality of semiconductor lasers, accordingly, an original driving circuit is provided for each semiconductor laser. For example, when 4 colors are used, four semiconductor lasers and four driving circuits are incorporated in the scanning unit, and the bias control and the APC control is performed in each driving circuit.
However, as described above, since the scanning unit and the controller are separately constructed, many signal lines are required between the scanning unit and the controller in accordance with the number of lasers. This causes complex circuit construction. Further, when using the plurality of signal lines, since image data signals and control signals influence each other, the bias control and the APC cannot be performed properly.
Therefore, an object of the present invention is to provide a multi-beam scanning apparatus that properly controls a plurality of light sources while using a single control signal line.
A multi-beam scanning apparatus according to the present invention has a scanning unit that has a plurality of semiconductor lasers and scans laser beams emitted from the plurality of semiconductor lasers; and a controller that transmits a standard signal associated with the control of the plurality of semiconductor lasers to the scanning unit. The controller has a standard signal generator that generates and outputs a sequence of pulse signals as the standard signal. The sequence of pulse signals has a plurality of common pulse signal sections that correspond to the plurality of semiconductor lasers. Each of the plurality of common pulse signal sections has a peculiar waveform characteristic depending upon the corresponding semiconductor laser. For example, each of the pulse signal sections has a peculiar duty ratio or frequency.
On the other hand, the scanning unit has a plurality of laser drivers, a standard voltage generator, and a standard voltage setter. The plurality of laser drivers drives a corresponding semiconductor laser among the plurality of semiconductor lasers in accordance with the standard signal. The standard voltage generator converts the sequence of pulse signals to a sequence of standard voltage signals that correspond to the plurality of semiconductor lasers and have a plurality of standard voltage sections. The standard voltage setter detects each of the plurality of common pulse signal sections in accordance with its signal wave characteristic, such as a frequency or a waveform, and that transmits each value of the plurality of standard voltage sections to a corresponding laser driver in accordance with the detected common pulse signal section. Each of the plurality of laser drivers controls the corresponding semiconductor laser in accordance with a value of a corresponding standard voltage section.
A multi-beam scanning apparatus according to another aspects of the present invention has a plurality of light sources, a plurality of driving circuits, an exposure unit, a controller, and a control value setter. The plurality of light sources respectively emit beam. The plurality of driving circuits corresponds to the plurality of light sources. Each driving circuit drives a corresponding light source. The exposure unit has an optical system and scans laser-beams emitted from the plurality of light sources. The controller generates a sequence of pulse signals corresponding to the plurality of light sources, the sequence of pulse signals being output via single control signal line. The control value setter sets a control value for each of the plurality of driving circuits in accordance with the sequence of pulse signals The plurality of driving circuits respectively drives the corresponding light source in accordance with the corresponding control value.
The multi-beam scanning apparatus according to another aspects of the present invention has a scanning unit, and a controller. The scanning unit has a plurality of semiconductor lasers and drives the plurality of semiconductor lasers separately. The controller generates a sequence of control signals and transmits the sequence of control signals to the scanning unit, the scanning unit being connected to the controller via a single control signal line for transmitting the sequence of control signals. The scanning unit detects a plurality of control values corresponding to the plurality of semiconductor lasers from the sequence of control signals, and drives each of the plurality of semiconductor lasers in accordance wish a corresponding control value.